Sputtering target, oxide semiconducting film, and method for making the same

ABSTRACT

An oxide semiconductor film includes indium (In), cerium (Ce), zinc (Zn), doping metal element (M) and oxygen (O) elements, and a molar ratio of the In, Ce, and Zn as In:Ce:Zn is in a range of 2:(0.5 to 2):1. A method for making a oxide semiconductor film includes a step of forming an oxide film on a substrate by using a sputtering method and a sputtering target comprising In 2 Ce x ZnO 4+2x , wherein x=0.5˜2.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims all benefits accruing under 35 U.S.C. §119 fromChina Patent Application No. 201510477921.1, filed on Aug. 6, 2015, inthe China Intellectual Property Office.

FIELD

The present disclosure relates to semiconductor manufacture.

BACKGROUND

Display devices should have high resolution, high response speed, lowenergy consumption, high transparency, and flexibility. These qualitiesdepend on performances of thin film transistors (TFTs) used in thedisplay devices. An amorphous silicon TFT has a relatively low carriermobility, which cannot meet the requirements of high resolution andlarge area display. A low temperature poly-silicon (p-Si) TFT can have ahigh mobility. However, a high cost is incurred in creating a large areadisplay device with the p-Si TFT. Recently, an amorphous oxidesemiconductor, indium gallium zinc oxide (InGaZnO₄, or IGZO), has beenproposed. An IGZO based TFT has a high transparency, a low manufacturingtemperature, and a good compatibility with the TFT manufacturingtechnology.

The mobility of the IGZO TFT is between that of the amorphous siliconTFT and the p-Si TFT, thus improvement is still required. An indium zincoxide (IZO) device, with high carrier density and a low stability, isnot a semiconductor but has a higher carrier mobility than that of IGZO.

BRIEF DESCRIPTION OF THE DRAWINGS

Implementations of the present technology will now be described, by wayof example only, with reference to the attached figures.

FIG. 1 is a flowchart of a method for making a sputtering target.

FIG. 2 is a flowchart of a method for making an oxide semiconductorfilm.

FIG. 3 is a schematic view of an embodiment of a TFT.

FIG. 4 shows an X-ray diffraction (XRD) pattern of the oxidesemiconductor film in Example 2-1 post.

FIG. 5 shows a Scanning Electron Microscope (SEM) image of the oxidesemiconductor film in Example 2-1.

FIG. 6 shows an SEM image of the oxide semiconductor film in Example2-2.

FIG. 7 shows an SEM image of the oxide semiconductor film in Example2-3.

DETAILED DESCRIPTION

It will be appreciated that for simplicity and clarity of illustration,where appropriate, reference numerals have been repeated among thedifferent figures to indicate corresponding or analogous elements. Inaddition, numerous specific details are set forth in order to provide athorough understanding of the embodiments described herein. However, itwill be understood by those of ordinary skill in the art that theembodiments described herein can be practiced without these specificdetails. In other instances, methods, procedures, and components havenot been described in detail so as not to obscure the related relevantfeature being described. Also, the description is not to be consideredas limiting the scope of the embodiments described herein. The drawingsare not necessarily to scale and the proportions of certain parts may beexaggerated to better illustrate details and features of the presentdisclosure.

Several definitions that apply throughout this disclosure will now bepresented.

The term “comprise” or “comprising” when utilized, means “include orincluding, but not necessarily limited to”; it specifically indicatesopen-ended inclusion or membership in the so-described combination,group, series, and the like. The term “contact” when utilized, means“direct contact” or “physical contact.”

One embodiment of a sputtering target comprises an indium cerium zincoxide represented by formula In₂Ce_(x)ZnO_(4+2x), wherein x=0.5˜2, andfurther comprises a doping metal element (M). In the sputtering target,an atom percentage of M in total metal element (i.e., In+Ce+Zn+M) is ina range from about 0.5% to about 1%.

The sputtering target can be obtained by sintering a mixture of indiumoxide (In₂O₃), cerium oxide (CeO₂), zinc oxide (ZnO), and doping metaloxide. In one embodiment, the sputtering target is obtained by sinteringonly the mixture of In₂O₃, CeO₂, ZnO, and the doping metal oxide.Impurities may exist in the mixture. Besides In₂O₃, CeO₂, ZnO, and thedoping metal oxide, the mixture may only comprise the impurities. Thesmaller the amount of the impurities in the mixture the better. In oneembodiment, the amount of the impurities can be less than 10 ppm.

The In₂Ce_(x)ZnO_(4+2x) is a crystal (or crystalline solid). Thesputtering target can also comprise a non crystalline (amorphous) solid.The amorphous solid comprises indium oxide, cerium oxide, and zincoxide. In one embodiment, a weight percentage of the crystallineIn₂Ce_(x)ZnO_(4+2x) in the sputtering target is above 80%.

In one embodiment, the sputtering target only comprisesIn₂Ce_(x)ZnO_(4+2x), In₂O₃, CeO₂, ZnO, and the doping metal oxide.Besides In₂Ce_(x)ZnO_(4+2x) (and In₂O₃, CeO₂, ZnO, the doping metaloxide if have), the sputtering target may only comprise unwanted andtrace amounts of impurities. The smaller the amount of impurities in thesputtering target the better. In one embodiment, the amount ofimpurities in the sputtering target can be less than 10 ppm.

The doping metal element has a relatively high field strength, lowelectronegativity, strong combine force to oxygen, and low tendency offorming oxygen vacancy. The doping metal element can be selected fromthe group consisting of Hf, Mg, Zr, Y, Mo, Sc, Al, Ti, Eu, andcombinations thereof.

A relative density of the sputtering target can be larger than or equalto 90%. The relative density is a ratio of a real density of thesputtering target to a theoretical density of In₂Ce_(x)ZnO₄₊₂.

A bulk resistance of the sputtering target can be in a range from about10⁻² Ωcm to about 10 Ωcm.

An average surface roughness of the sputtering target can be less thanor equal to 2 microns, and in one embodiment be less than or equal to0.5 microns.

An average flexural strength of the sputtering target can be larger thanor equal to 50 MPa, and in one embodiment be larger than or equal to 55MPa.

FIG. 1 presents a flowchart in accordance with an illustrated exampleembodiment. The embodiment of a method 100 for making the sputteringtarget is provided by way of example, as there are a variety of ways tocarry out the method 100. Each block shown in FIG. 1 represents one ormore processes, methods, or subroutines carried out in the exemplarymethod 100. Additionally, the illustrated order of blocks is by exampleonly and the order of the blocks can be changed. The exemplary method100 can begin at block 101. Depending on the embodiment, additionalsteps can be added, others removed, and the ordering of the steps can bechanged.

At block 101, the In₂O₃ powder, CeO₂ powder, ZnO powder, and dopingmetal oxide powder are mixed to form a mixture. In the mixture, a molarratio of indium (In), cerium (Ce), and zinc (Zn) as In:Ce:Zn issubstantially 2:(0.5 to 2):1.

At block 102, the mixture is sintered at a temperature in a range fromabout 1250° C. to about 1650° C.

In the mixture, an atom percentage of doping metal element (M) in totalmetal element (i.e., In+Ce+Zn+M) is in a range from about 0.5% to about1%.

In the mixture, the In₂O₃ powder, CeO₂ powder, ZnO powder, and dopingmetal oxide powder can respectively have an average diameter that isless than or equal to 10 microns. In one embodiment, the averagediameter of the In₂O₃ powder, CeO₂ powder, ZnO powder, and doping metaloxide powder can respectively be in a range from about 0.5 microns toabout 2 microns.

The purity of the In₂O₃ powder, CeO₂ powder, ZnO powder, and dopingmetal oxide powder can be 3N (99.9 mass %) to 5N (99.999%).

A molar ratio of the In₂O₃ powder, CeO₂ powder, and ZnO powder asIn₂O₃:CeO₂:ZnO is substantially 2:(1 to 4):2.

The doping metal oxide can be selected from HfO₂, MgO, ZrO₂, Y₂O₃, MoO₃,Sc₂O₃, Al₂O₃, TiO₂, Eu₂O₃, and combinations thereof.

The In₂O₃ powder, CeO₂ powder, ZnO powder, and doping metal oxide powdercan be mixed in air or in a protective atmosphere (e.g., in argon (Ar)or nitrogen (N₂) gas). The mixing of the In₂O₃ powder, CeO₂ powder, ZnOpowder, and doping metal oxide powder can further comprise steps of:ball milling the In₂O₃ powder, CeO₂ powder, ZnO powder, and doping metaloxide powder together in a liquid medium to form a mixed substance;drying the mixed substance to remove the liquid medium to obtain themixture that is dry. The liquid medium is not reactive with the In₂O₃powder, CeO₂ powder, ZnO powder, and doping metal oxide powder and canbe removed from the wet mixed substance by a drying step, and brings noimpurity substance into the mixture. The liquid medium can be water,ethanol, acetone, or combinations thereof. The ball milling can takeplace in a ball milling machine. The liquid medium, In₂O₃ powder, CeO₂powder, ZnO powder, and doping metal oxide powder are introduced intothe ball milling machine. A rotating speed of the ball milling machinecan be about 100 rpm to about 600 rpm. During the ball milling, theIn₂O₃ powder, CeO₂ powder, ZnO powder, and doping metal oxide powder mixuniformly, the particle diameters of the powders can decrease, and thespecific surface area of the particles of the powders can increase.

The ball milling can last until the In₂O₃ powder, CeO₂ powder, ZnOpowder, and doping metal oxide powder are uniformly mixed and theparticle diameters of the powders have decreased to the desired sizes.The mixed substance is taken out from the ball milling machine anddried, for example at about 30° C. to about 60° C., to remove the liquidmedium. The mixed substance can be dried in air or a protectiveatmosphere (e.g., Ar gas or N₂ gas). In one embodiment, the mixedsubstance is dried at a high purity (3N to 5N) of protective gas.

The mixture can be sintered in a protective atmosphere (e.g., in argon(Ar) or nitrogen (N₂) gas).

The mixture can be molded or pressed into a desired shape before orduring the sintering step. During the sintering step, the In₂O₃ powder,CeO₂ powder, and ZnO powder react to form the crystalline solidIn₂Ce_(x)ZnO_(4+2x). The doping metal oxide is doped in the crystallineIn₂Ce_(x)ZnO_(4+2x).

A hot pressing method or a hot isostatic pressing (HIP) method can beused to simultaneously mold/press and sinter the mixture. The hotpressing applies a pressure of about 30 MPa to 100 MPa at thetemperature of about 1250° C. to about 1650° C. for about 1 hour toabout 24 hours. The hot isostatic pressing applies a pressure of about100 MPa to 300 MPa at the temperature of about 1250° C. to about 1650°C. for about 1 hour to about 40 hours.

When the sintering step takes place after the molding/pressing step, themolding/pressing step can be processed by using a cold pressing methodor a cold isostatic pressing method. The mixture can be filled into amold and molded/pressed by applying a pressure of about 30 MPa to about300 MPa to form the desired shape. The mixture with the desired shapecan be sintered under normal pressure.

The sputtering target can be obtained directly from the sintering step.In another embodiment, the product of the sintering step can be shapedor polished to form the sputtering target.

One embodiment of an oxide semiconductor film comprises In, Ce, Zn,doping metal element (M) and O elements, wherein a molar ratio of In,Ce, and Zn as In:Ce:Zn is 2:(0.5 to 2):1, and an atom percentage of M intotal metal element (i.e., In+Ce+Zn+M) is in a range from about 0.5% toabout 1%. The oxide semiconductor film is an n-type semiconductor havinga carrier density of about 10¹² cm⁻³ to about 10²⁰ cm⁻³, and a carriermobility of about 5.0 cm² V⁻¹ s⁻¹ to about 46.3 cm² V⁻¹ s⁻¹.

The oxide semiconductor film can be an amorphous solid. In anotherembodiment, the oxide semiconductor film can also comprise crystallinesolid In₂Ce_(x)ZnO₄₊₂,

M can be selected from the group consisting of Hf, Mg, Zr, Y, Mo, Sc,Al, Ti, Eu, and combinations thereof.

In one embodiment, unwanted and trace impurities are the only substancein the oxide semiconductor film beyond the elements of In, Ce, Zn, M andO. The smaller the amount of impurities in the sputtering target thebetter. In one embodiment, the amount of impurities in the oxidesemiconductor film can be less than 10 ppm.

The oxide semiconductor film can have a band gap of about 3.0 eV toabout 3.5 eV.

The oxide semiconductor film can have a visible light transmittance ofabout 60% to about 90%.

The oxide semiconductor film can have a thickness of about 50 nm toabout 1000 nm.

The oxide semiconductor film can have a carrier density of about 10¹³cm⁻³ to about 10¹⁵ cm⁻³.

The oxide semiconductor film can have a carrier mobility of about 12.3cm² V⁻¹ s⁻¹ to about 46.3 cm² V⁻¹ s⁻¹.

The oxide semiconductor film can be obtained by a sputtering methodusing the sputtering target as described above.

FIG. 2 reveals one embodiment of a method 200 for making the oxidesemiconductor film, comprising a step of sputtering an oxide film on asubstrate by the sputtering method using the sputtering target asdescribed above, as shown in block 201.

The sputtering method can be a DC (direct current) sputter method, an AC(alternating current) sputter method, an RF (radio frequency) sputtermethod, a magnetron sputter method, or a medium frequency magnetronsputter method. The current of the sputtering can be about 0.1 A toabout 2.0 A. The sputtering can take place for about 1 minute to about120 minutes.

The sputtering can be at room temperature or a high temperature (e.g.,smaller than or equal to 400° C.). When the high temperature is used inthe sputtering, the method 200 further comprises a step of preheatingthe substrate. The substrate can be previously heated in vacuum at atemperature of about 50° C. to about 400° C.

A carrier gas is introduced into the sputtering chamber during thesputtering. The carrier gas can be a noble gas, a mixture of a noble gasand oxygen gas, or a mixture of a noble gas and hydrogen gas. In oneembodiment, the noble gas can be Ar gas. For example, the carrier gascan be a mixture of Ar gas and oxygen gas. A flow rate of the oxygen gascan be less than 3 sccm. A purity of the carrier gas can be 3N to 5N.

The pressure in the sputtering chamber during the sputtering can beabout 0.1 Pa to about 2.0 Pa.

The substrate can be an insulating substrate capable of enduring thesputtering temperature. Glass, silicon, or polymer (PET, PI, PE, etc.)can be used as the substrate. When the sputtering is at a relatively lowtemperature (e.g., at room temperature), the choice of the substratematerial is wide.

Before the sputtering, the substrate can be previously cleaned to removeimpurities on the surface of the substrate.

Before the sputtering, the sputtering target can be fixed on a support.An outer surface of the sputtering target can be parallel to the surfaceof the substrate. In another embodiment, an angle can be formed betweenthe outer surface of the sputtering target and the surface of thesubstrate, the angle can be 20° to 85°. A distance between the outersurface of the sputtering target and the surface of the substrate can besmaller than or equal to 8 cm.

The oxide film formed on the surface of the substrate in block 201 canbe directly used as the oxide semiconductor film. In another embodiment,the method can also comprise the annealing step shown in block 202.

In block 202, the oxide film can be annealed in a vacuum, or in an N₂ ornoble gas (e.g., Ar gas) atmosphere. The background vacuum used in theannealing can be about 10 ⁻³ Pa to about 10 Pa. The annealingtemperature can be in a range from about 100° C. to about 400° C. Aspeed of temperature increase can be in a range from about 1° C./min toabout 20° C./min to increase the temperature of the oxide film to theannealing temperature. The oxide film can be annealed for about 1 hourto about 10 hours. The annealing step can slightly increase thecrystallization of the oxide film to adjust the performance of the oxidesemiconductor film.

The carrier density of the n-type oxide semiconductor film can be about10¹² cm⁻³ to about 10²⁰ cm⁻³, and the carrier mobility of the n-typeoxide semiconductor film can be about 5.0 cm² V⁻¹ s⁻¹ to about 46.3 cm²V^('1) s⁻¹. The n-type oxide semiconductor film can be used in an n-typeTFT. The amount of Ce in the oxide semiconductor film cannot be toolarge or too small. When x<0.5, the oxide semiconductor film hasproperties similar to those of IZO, which has a relatively lowstability, and thus not proper as a TFT semiconductor. When x>2, theoxide semiconductor film has a relatively low carrier mobility that isnot suitable for high resolution display devices. The doping metalelement (M) is introduced to further decrease the oxygen vacancy in theoxide semiconductor film, thus further improves the stability of thedevice using the oxide semiconductor film, such as the TFT, especiallythe stabilities under electrical bias and light illumination.

One embodiment of a semiconducting device comprises the above describedoxide semiconductor film.

Referring to FIG. 3, one embodiment of a thin film transistor 10comprises an insulating substrate 110, a semiconducting layer 140, asource electrode 151, a drain electrode 152, a gate electrode 120, and ainsulating layer 130. The source electrode 151 and the drain electrode152 are spaced from each other. The semiconducting layer 140 iselectrically connected between the source electrode 151 and the drainelectrode 152. The gate electrode 120 is insulated from thesemiconducting layer 140, the source electrode 151, and the drainelectrode 152 by the insulating layer 130. The semiconducting layer 140can be the above described oxide semiconductor film. The thin filmtransistor 10 can be conventional except the semiconducting layer. Thethin film transistor 10 can be a top gate structure as shown in FIG. 3,or a bottom gate structure.

EXAMPLE 1 Sputtering Target EXAMPLE 1-1-1

209 g of In₂O₃ powder, 260 g of CeO₂ powder and 61 g of ZnO powder witha molar ratio as In₂O₃:CeO₂:ZnO is 1:2:1, and HfO₂ powder all havingpurities of 4N are mixed in a ball milling machine having water as theliquid medium, at a rotating speed of about 200 rpm for about 10 hours.The atom percentage of Hf in total metal element (i.e., In+Ce+Zn+Hf) is0.5%. After that, the mixed substance is dried at a pressure of about 1atm in an Ar gas atmosphere (5N) for about 1 hour to remove the water.The mixture is hot pressed in Ar gas atmosphere at a pressure of about50 MPa and a temperature of about 1350° C. for about 5 hours with aspeed of temperature increase of about 15° C./min. The obtainedsputtering target has a relative density >87% and a bulk resistance of0.70 Ωcm˜0.86 Ωcm.

EXAMPLE 1-1-2

This example is the same as Example 1-1-1 except that the HfO₂ powder isreplaced with ZrO₂. The atom percentage of Zr in total metal element(i.e., In+Ce+Zn+Zr) is 0.5%.

EXAMPLE 1-2-1

249 g of In₂O₃ powder, 231 g of CeO₂ powder and 73 g of ZnO powder witha molar ratio as In₂O₃:CeO₂:ZnO is 2:3:2, and HfO₂ powder all havingpurities of 4N are mixed in a ball milling machine having ethanol as theliquid medium at a rotating speed of about 400 rpm for about 20 hours.The atom percentage of Hf in total metal element (i.e., In+Ce+Zn+Hf) is0.5%. After that, the mixed substance is dried at a pressure of about 1atm in an Ar gas atmosphere (5N) for about 1 hour to remove the ethanol.The mixture is placed in a mold and cold pressed at a pressure of about75 MPa for about 60 minutes. The molded mixture is sintered at a normalpressure in N₂ gas atmosphere (5N) at a temperature of about 1450° C.for about 8 hours with a speed of temperature increase of about 10°C./min. The obtained sputtering target has a relative density >85% and abulk resistance of 0.12 Ωcm˜0.34 Ωcm.

EXAMPLE 1-2-2

This example is the same as Example 1-2-1 except that the HfO₂ powder isreplaced with ZrO₂. The atom percentage of Zr in total metal element(i.e., In+Ce+Zn+Zr) is 0.5%.

EXAMPLE 1-3-1

209 g of In₂O₃ powder, 260 g of CeO₂ powder and 61 g of ZnO powder witha molar ratio as In₂O₃:CeO₂:ZnO is 1:2:1, and HfO₂ powder all havingpurities of 4N are mixed in a ball milling machine having water as theliquid medium at a rotating speed of about 500 rpm for about 10 hours.The atom percentage of Hf in total metal element (i.e., In+Ce+Zn+Hf) is0.5%. After that, the mixed substance is dried at a pressure of about 1atm in an Ar gas atmosphere (5N) for about 1 hour to remove the water.The mixture is hot isostatically pressed in Ar gas atmosphere (5N) at apressure of about 100 MPa and a temperature of about 1450° C. for about20 hours with a speed of temperature increase of about 10° C./min. Theobtained sputtering target has a relative density >86% and a bulkresistance of 0.65 Ωcm˜0.78 Ωcm.

EXAMPLE 1-3-2

This example is the same as Example 1-3-1 except that the HfO₂ powder isreplaced with ZrO₂. The atom percentage of Zr in total metal element(i.e., In+Ce+Zn+Zr) is 0.5%.

EXAMPLE 2 Oxide Semiconductor Film EXAMPLE 2-1-1

A glass substrate is cleaned and dried by N₂ gas blowing. The glasssubstrate and the sputtering target of Example 1-1-1 are disposed in asputtering chamber. The surfaces of the sputtering target and thesubstrate are parallel to each other about 8 cm distant. The carriergas, which is Ar gas in this example, is introduced into the sputteringchamber. The Ar gas has a flow rate of about 40 sccm. The pressure inthe sputtering chamber is about 0.7 Pa. The sputtering is at roomtemperature by using a current of about 1.0 A for about 28 minutes toform the oxide semiconductor film with a thickness of about 250 nm. TheXRD pattern of the oxide semiconductor film is shown in FIG. 4 showingthat the oxide semiconductor films are amorphous films. The surfacemorphology of the oxide semiconductor film is shown in FIG. 5.

EXAMPLE 2-1-2

This example is the same as Example 2-1-1 except that the sputteringtarget is replaced with Example 1-1-2.

EXAMPLE 2-1-3

This example is the same as Example 2-1-1 except that the carrier gas isa combination of Ar gas and O₂ gas. The O₂ gas has a flow rate of about0.5 sccm.

EXAMPLE 2-1-4

This example is the same as Example 2-1-2 except that the carrier gas isa combination of Ar gas and O₂ gas. The O₂ gas has a flow rate of about0.5 sccm.

EXAMPLE 2-1-5

This example is the same as Example 2-1-1 except that the O₂ gas has aflow rate of about 1.0 sccm.

EXAMPLE 2-1-6

This example is the same as Example 2-1-2 except that the O₂ gas has aflow rate of about 1.0 sccm.

Hall tests are conducted on the oxide semiconductor films of Examples2-1, and reveal that the Hall mobility of the oxide semiconductor filmsare about 13.5 cm² V⁻¹ s⁻¹ to about 26.3 cm^(2 V) ⁻¹ s⁻¹, and thecarrier densities of the oxide semiconductor films are about 10¹³ cm⁻³to about 10²⁰ cm⁻³. The Hall mobility and carrier densities of the oxidesemiconductor films of Examples 2-1 change with the O₂ gas flow ratesare shown in Table 1.

EXAMPLE 2-2-1

A glass substrate is cleaned and dried by N₂ gas blowing. The glasssubstrate and the sputtering target of Example 1-2-1 are disposed in asputtering chamber. The surfaces of the sputtering target and thesubstrate are parallel to each other at about 8 cm distant. Thesubstrate is preheated to about 250° C. The carrier gas, which is Ar gasin this example, is introduced into the sputtering chamber. The Ar gashas a flow rate of about 40 sccm. The pressure in the sputtering chamberis about 0.7 Pa. The sputtering is at 250° C. by using a current ofabout 1.0 A for about 28 minutes to form the oxide semiconductor filmwith a thickness of about 250 nm. The surface morphology of the oxidesemiconductor film is shown in FIG. 6.

EXAMPLE 2-2-2

This example is the same as Example 2-2-1 except that the sputteringtarget is replaced with Example 1-2-2.

EXAMPLE 2-2-3

This example is the same as Example 2-2-1 except that the carrier gas isa combination of Ar gas and O₂ gas. The O₂ gas has a flow rate of about1 sccm.

EXAMPLE 2-2-4

This example is the same as Example 2-2-2 except that the carrier gas isa combination of Ar gas and O₂ gas. The O₂ gas has a flow rate of about1 sccm.

EXAMPLE 2-2-5

This example is the same as Example 2-2-1 except that the O₂ gas has aflow rate of about 2 sccm.

EXAMPLE 2-2-6

This example is the same as Example 2-2-2 except that the O₂ gas has aflow rate of about 2 sccm.

Hall tests are conducted on the oxide semiconductor films of Examples2-2, and reveals that the Hall mobility of the oxide semiconductor filmsare about 18.7 cm² V⁻¹ s⁻¹ to about 46.3 cm²V⁻¹ s⁻¹, and the carrierdensities of the oxide semiconductor films are about 10¹⁵ cm⁻³ to about10²⁰ cm⁻³. The Hall mobility and carrier densities of the oxidesemiconductor films of Examples 2-2 change with the O₂ gas flow ratesare shown in Table 1.

EXAMPLE 2-3-1

A glass substrate is cleaned and dried by N₂ gas blowing. The glasssubstrate and the sputtering target of Example 1-3-1 are disposed in asputtering chamber. The surfaces of the sputtering target and thesubstrate are parallel to each other at about 8 cm distant. The carriergas, which is Ar gas in this example, is introduced into the sputteringchamber. The Ar gas has a flow rate of about 40 sccm. The pressure inthe sputtering chamber is about 0.7 Pa.

The sputtering is at room temperature by using a current of about 1.0 Afor about 28 minutes to form the oxide semiconductor film with athickness of about 250 nm. The oxide semiconductor film is then annealedan atmospheric pressure of 1 Pa for about 1 hour. The annealingtemperature is about 150° C. The surface morphology of the oxidesemiconductor film is shown in FIG. 7.

EXAMPLE 2-3-2

This example is the same as Example 2-3-1 except that the sputteringtarget is replaced with Example 1-3-2.

EXAMPLE 2-3-3

This example is the same as Example 2-3-1 except that the annealingtemperature is about 250° C.

EXAMPLE 2-3-4

This example is the same as Example 2-3-2 except that the annealingtemperature is about 250° C.

EXAMPLE 2-3-5

This example is the same as Example 2-3-1 except that the annealingtemperature is about 350° C.

EXAMPLE 2-36

This example is the same as Example 2-3-2 except that the annealingtemperature is about 350° C.

Hall tests are conducted on the oxide semiconductor films of Examples2-3 before and after the annealing step. Before being annealed, the Hallmobility of the oxide semiconductor films reach about 20.3 cm² V⁻¹ s⁻¹,and the carrier densities of the oxide semiconductor films reach about10²⁰ cm⁻³. After being annealed, the Hall mobility of the oxidesemiconductor films are about 15.5 cm² V⁻¹ s⁻¹ to about 23.7 cm² V⁻¹s⁻¹, and the carrier densities of the oxide semiconductor films areabout 10¹⁴ cm⁻³ to about 10¹⁹ cm⁻³. The Hall mobility and carrierdensities of the oxide semiconductor films of Examples 2-3 change withthe annealing temperatures are shown in Table 1.

TABLE 1 Doping O₂ gas annealing metal flow rate temperature Hallmobility carrier density Example In:Ce:Zn element (sccm) (° C.)(cm²V⁻¹s⁻¹) (cm⁻³) 2-1-1 2:2:1 Hf 0 — 20.3 5.21 × 10¹⁸ 2-1-2 2:2:1 Zr 0— 19.1 3.75 × 10¹⁸ 2-1-3 2:2:1 Hf 0.5 — 26.3 1.25 × 10²⁰ 2-1-4 2:2:1 Zr0.5 — 25.7 1.12 × 10²⁰ 2-1-5 2:2:1 Hf 1 — 15.6 1.05 × 10¹⁴ 2-1-6 2:2:1Zr 1 — 13.5 8.72 × 10¹³ 2-2-1 4:3:2 Hf 0 — 32.4 5.27 × 10¹⁹ 2-2-2 4:3:2Zr 0 — 29.7 3.56 × 10¹⁹ 2-2-3 4:3:2 Hf 1 — 46.3 6.63 × 10²⁰ 2-2-4 4:3:2Zr 1 — 43.1 5.16 × 10²⁰ 2-2-5 4:3:2 Hf 2 — 20.2 2.11 × 10¹⁶ 2-2-6 4:3:2Zr 2 — 18.7 3.42 × 10¹⁵ 2-3-1 2:2:1 Hf 0 150 23.7 1.08 × 10¹⁹ 2-3-22:2:1 Zr 0 150 22.6 8.81 × 10¹⁸ 2-3-3 2:2:1 Hf 0 250 19.7 2.79 × 10¹⁷2-3-4 2:2:1 Zr 0 250 18.5 9.34 × 10¹⁶ 2-3-5 2:2:1 Hf 0 350 16.1 5.41 ×10¹⁴ 2-3-6 2:2:1 Zr 0 350 15.5 3.17 × 10¹⁴

Depending on the embodiment, certain of the steps of methods describedmay be removed, others may be added, and the sequence of steps may bealtered. It is also to be understood that the description and the claimsdrawn to a method may comprise some indication in reference to certainsteps. However, the indication used is only to be viewed foridentification purposes and not as a suggestion as to an order for thesteps.

The embodiments shown and described above are only examples. Even thoughnumerous characteristics and advantages of the present technology havebeen set forth in the foregoing description, together with details ofthe structure and function of the present disclosure, the disclosure isillustrative only, and changes may be made in the detail, especially inmatters of shape, size, and arrangement of the parts within theprinciples of the present disclosure, up to and including the fullextent established by the broad general meaning of the terms used in theclaims. It will therefore be appreciated that the embodiments describedabove may be modified within the scope of the claims.

What is claimed is:
 1. An oxide semiconductor film comprising indium(In), cerium (Ce), zinc (Zn), doping metal element (M) and oxygen (O)elements, a molar ratio of In, Ce, and Zn as In:Ce:Zn is in a range of2:(0.5 to 2):1, a carrier density of about 10¹² cm⁻³ to about 10²⁰ cm⁻³,and a carrier mobility of about 5.0 cm2V⁻¹ s⁻¹ to about 46.3 cm² V⁻¹s⁻¹, and the oxide semiconductor film is an n-type semiconductor.
 2. Theoxide semiconductor film of claim 1 being an amorphous film.
 3. Theoxide semiconductor film of claim 1, wherein an atom percentage of M intotal metal element is in a range from about 0.5% to about 1%.
 4. Theoxide semiconductor film of claim 1, wherein M is selected from thegroup consisting of Hf, Mg, Zr, Y, Mo, Sc, Al, Ti, Eu, and combinationsthereof.
 5. A sputtering target comprising an oxide represented byIn₂Ce_(x)ZnO_(4+2x), wherein x=0.5˜2, and further comprising a dopingmetal element (M).
 6. The sputtering target of claim 5, wherein an atompercentage of M in total metal element is in a range from about 0.5% toabout 1%.
 7. The sputtering target of claim 5, wherein M is selectedfrom the group consisting of Hf, Mg, Zr, Y, Mo, Sc, Al, Ti, Eu, andcombinations thereof.
 8. A method for making a sputtering targetcomprising: mixing indium oxide (In₂O₃) powder, cerium oxide (CeO₂)powder, zinc oxide (ZnO) powder, and doping metal oxide powder to form amixture, a molar ratio of indium (In), cerium (Ce), and zinc (Zn) asIn:Ce:Zn in the mixture is 2:(0.5 to 2):1; and sintering the mixture ata temperature in a range from about 1250° C. to about 1650° C.
 9. Themethod of claim 8, wherein the doping metal oxide powder is selectedfrom HfO₂, MgO, ZrO₂, Y₂O₃, MoO₃, Sc₂O₃, Al₂O₃, TiO₂, Eu₂O₃, andcombinations thereof.
 10. The method of claim 8, wherein the sinteringcomprises using a hot pressing method or a hot isostatic pressing methodto simultaneously press and sinter the mixture, the hot pressing methodcomprises applying a pressure of about 30 MPa to 100 MPa at thetemperature of about 1250° C. to about 1650° C. for about 1 hour toabout 24 hours to the mixture, the hot isostatic pressing methodcomprises applying a pressure of about 100 MPa to 300 MPa at thetemperature of about 1250° C. to about 1650° C. for about 1 hour toabout 40 hours to the mixture.
 11. The method of claim 8 furthercomprising pressing the mixture into a desired shape before thesintering, and the pressing comprising applying a pressure of about 30MPa to about 300 MPa to the mixture.
 12. The method of claim 8, whereinthe sintering takes place in a protective gas.